In general, various kinds of pressures are applied to a photographic light-sensitive material formed by coating silver halide emulsion(s) on a support. For example, a photographic negative film is generally rolled into a cartridge and is loaded into a camera, and in these cases the film is bent or pulled for advancing it in the camera.
On the other hand, since sheet film such as photographic light-sensitive films for printing and direct medical radiographic light-sensitive films are handled directly, it frequently occurs that the sheet films are broken or curved in these cases.
Also, large pressures are applied to photographic light-sensitive materials during the cutting and working thereof.
If these various pressures are applied to photographic light-sensitive materials, the pressures are applied to the silver halide grains through gelatin as a binder for the silver halide grains and a plastic film as the support thereof.
It is known that when pressures are applied to silver halide grains, the photographic characteristics of the silver halide materials are changed as reported, for example, in K. B. Mather, Journal of Optical Society of America, 38, 1054 (1948), P. Faelens and P. de Smet, Scie. et Ind. Phot., 25, No. 5, 178 (1954), and P. Faelens, Journal of Photographic Science, 2, 105 (1954).
Accordingly, it has been earnestly desired to provide a photographic light-sensitive material, the photographic properties of which are not adversely influenced by such pressures.
As a means for improving the pressure characteristics of photographic light sensitive materials, it is known to prevent these pressures from affecting silver halide grains by incorporating a plasticizer such as a polymer or an emulsified material in the photographic light-sensitive materials or reduce the silver halide/gelatin ratio of the silver halide emulsion.
For example, British Patent 738,618 discloses a method of using a heterocyclic compound, British Patent 738,637 an alkylphthalate, British Patent 730,030 an alkyl ester, U.S. Pat. No. 2,960,404 a polyhydric alcohol, U.S. Pat. No. 3,121,060 a carboxyalkyl cellulose, JP-A-49-5017 a paraffin and a carboxylate, and JP-B-28086 an alkylacrylate and an organic acid (the term "JP-A" as used herein means an "unexamined published patent application", and "JP-B" as used herein means an "examined published Japanese patent application").
However, in the method of using a plasticizer, the amount that can be used is limited because the plasticizer reduces the mechanical strength of the silver halide photographic emulsion layers containing it and if the amount of gelatin is increased accordingly to prevent the reduction of the layer strength, the photographic processing speed of the photographic light-sensitive materials containing the emulsion is delayed. Thus, the aforesaid methods do not provide satisfactory results.
On the other hand, recently, the sensitivity of silver halide photographic materials has been dramatically increased and the photographic materials have been reduced in size.
Thus, a photographic light-sensitive material having a higher sensitivity and giving excellent image quality has been strongly desired.
Accordingly, the desire for silver halide emulsions for photography which have superior photographic performance in terms of high sensitivity, high contrast, excellent graininess, and excellent sharpness has increased. To this end, techniques of producing and using tabular grain silver halide emulsions aimed at increasing sensitivity including the increase of the color sensitizing effect by sensitizing dye, the improvement of the relation of sensitivity/graininess, and improvement of sharpness, and the improvement of covering power are disclosed in U.S. Pat. Nos. 4,386,156, 4,504,570, 4,478,929, 4,414,304, 4,411,986, 4,400,463, 4,414,306, 4,439,520, 4,433,048, 4,434,226, 4,413,053, 4,439,353, 4,490,458, and 4,399,215.
In general, hexahedral, octahedral or potato-like silver halide grains have been known to be susceptible to deformation by external forces as compared to the tabular silver halide grain having a large diameter/thickness ratio.
However, in general, tabular silver halide grains having a large diameter/thickness ratio (aspect ratio) have also proven very weak to external pressure and thus have not provided satisfactory pressure resistant characteristics.
For example, if tabular silver halide grains are formed by adding silver nitrate to an aqueous solution containing gelatin, potassium bromide, and potassium iodide, the silver halide emulsion obtained has greatly reduced sensitivity due to the action of external pressure and hence is very inconvenient for practical and commercial use.
On the other hand, the aforesaid tendency of causing desensitization by the action of external pressure can be improved in pure silver bromide grains or silver iodobromide grains composed of a completely uniform halogen composition throughout the whole grain formed by adding an aqueous silver nitrate solution and an aqueous solution of halides to an aqueous gelatin solution by a double jet method so that the re growth of nuclei does not occur. However, these silver halide grains are very liable to fog by the action of external pressure and hence are undesirable for practical use.
U.S. Pat. No. 2,592,250 discloses a silver halide emulsion formed by subjecting silver chloride emulsion grains to a halogen conversion using bromide ions or iodide ions. JP-B-50-36978 discloses a method of using the aforesaid silver halide emulsion, the surface of which has been chemically sensitized. JP-A-61-122641 discloses a silver halide emulsion formed by subjecting an emulsion containing chloride ions to a halogen conversion using bromide ions or iodide ions in the presence of a solvent. Also, JP-A-51-2417 discloses a method of growing silver halide grains by adding bromide ions or iodide ions to a silver halide emulsion within 20 minutes after the formation of the silver chloride grains and then physically ripening them.
However, in the aforesaid production method for silver halide grains, it is virtually impossible to control the form of the grains and as described in the aforesaid patents and patent applications, the sizes and forms of the silver halide grains are completely changed by the halogen conversion. Accordingly, it is difficult to apply such a technique to the formation of tabular silver halide grains.
JP-B-61-31454 discloses a method of depositing silver bromide on silver chloride grains not in a halogen conversion type but in a laminated layer type.
JP-A-58-111936 and U.S. Pat. No. 4,414,306 disclose a method of obtaining tabular silver chlorobromide grains by growing silver chlorobromide at the annular domains of tabular silver bromide grains. However, in the tabular grains obtained by this method, some properties of the silver chloride produced such as the fast developing property, etc., may be obtained; however the tabular grains have a problem that the properties of silver iodobromide itself, such as the improved relation of sensitivity and graininess, etc., are lost.
JP-A-59-99433 discloses that the pressure resistant characteristics of tabular silver halide grains are improved by forming a high iodide-containing layer in the interior of the tabular grains. JP-A-61-14636 discloses that the pressure resisting characteristics of tabular silver halide grains can be improved by increasing the iodide content in the central domain of the tabular grains over that in the outer domain thereof. Also, Japanese Patent Application No. 62-54640 discloses a method of introducing dislocation lines in the annular domains of the tabular grains by iodide ions. However, although the aforesaid methods of using iodide ions may improve the pressure resistant characteristics, at the same time, they adversely influence photographic characteristics such as developing property, etc., and hence they are restricted in their use.
Also, it is known that a mono-dispersed emulsion is excellent for providing a high sensitivity, high contrast, and excellent graininess. However, this type of emulsion has not been satisfactory in regard to the pressure resistant characteristics. Various methods have been proposed to remedy this problem.
For example, as a method of using iodide ions, JP A-59-178447 discloses a silver halide photographic of emulsion locally containing iodide ions. Also, U.S. Pat. No. 4,210,450 discloses a method of producing silver halide grains halogen-converted by iodide ions during the formation of the grains as described hereinabove. However, although methods of using iodide ions may improve the pressure resistant characteristics of the silver halide emulsion, they adversely influence the photographic characteristics thereof, such as the developing property, etc., thereof and hence the use of such methods is restricted.
On the other hand, as a method of using silver chloride, U.S. Pat. No. 4,495,277 discloses a silver halide emulsion having a silver chloride layer as one layer in the inside nucleus of the silver halide grains. However, although this method may improve the pressure resistant properties, it causes the deterioration of the graininess thereof.
Furthermore, for the requirements of a photographic light-sensitive material to have a high sensitivity excellent image quality, JP-A-60-143331 discloses that a silver halide emulsion having a high sensitivity, excellent graininess and causing less fog is obtained by forming silver halide grains having a clear double structure and increasing the iodine content in the core portion thereof. Also, it is known that the absorption of dyes onto silver halide grains is increased by increasing the iodine content at the surface portion thereof as described, for example, in T. H. James, The Theory of the Photographic Process, page 241. This technique is also convenient for color sensitization. Also, a silver halide emulsion having a high content of iodide in the surface portions of the silver halide grains shows a large edge effect and is effective in providing photographic light-sensitive material having excellent image sharpness.
However, the silver halide emulsion having high iodide content at the surface portions of the grains generally shows pressure fog and pressure sensitization, and hence a counterplan therefor has been required.